The recent rise in popularity of smart phones is changing the way people use their wireless devices and how services are offered. For example, location based services are becoming more and more the norm. Likewise, social media applications employing location information are emerging and are expected to grow in use in the near future. It is expected that applications and services involving two or more nearby devices may cause large amount of data traffic in networks. One approach to mitigate the increase in network traffic due to these “Proximity Services” may be to limit the traffic to the cell, for example allowing direct User Equipment (UE)-to-UE and/or device-to-device (D2D) communications and/or to have the eNode-B (eNB) relay the information. This last option reduces the data traffic on the network as the data packets may no longer be carried to the SGSN and back to the originating eNB, thereby offloading the network. This local offload approach may be used when large amount of data is to be exchanged.
The spectacular increase in wireless data services in recent years can be partially attributed to the improvement in radio communications technology. More particularly, the use of link-adaptation has had a large impact on the spectrum efficiency and the improvement in the offered data rates. In mobile wireless communications, the propagation channel experiences fades which varies in time due to the device mobility. Due to this fast fading, the quality of the channel varies and likewise the amount of data that can be carried reliably varies in time. Fast link adaptation allows the transmitter to adapt the amount of data as a function of the channel quality thereby improving the overall spectrum efficiency.
At a high level, link adaptation between, for example, a user's handset and an eNB may entail the transmitter and/or the scheduler determining the characteristics of the propagation channel (also referred to as channel state information or CSI). In practice, this may be implemented via the receiver sending CSI feedback to the transmitter; although sometimes this CSI can be inferred, at least partially, in different ways (e.g. via reciprocity in the case of TDD). In traditional systems such as LTE/LTE-A, HSPA, 802.11, 802.16 and others, the receiver measures the propagation channel and sends the CSI back to the transmitter (in the case of the uplink) so that the scheduling can take advantage of the channel conditions.